程序代做CS代考 c++ Haskell # Abstract syntax – cscodehelp代写

# Abstract syntax

A video on this section can be found [here](https://bham.cloud.panopto.eu/Panopto/Pages/Viewer.aspx?id=78c83470-4c37-4279-bef8-ac85012e8be3).

The operations are listed in the order of precedence as in the
languages C and C++ (from low to high), where all the operations in
the same line have the same precedence, but this is important for
[parsing](Parser.md) only:

“`haskell
module AbstractSyntax where

type Identifier = String

data OpName = Or — ||
| And — &&
| Eq — ==
| Leq | Less | Geq | Greater — <= < >= >
| Add | Sub — + –
| Mul | Div | Mod — * / %
| Not — !
deriving (Show)

data Expr = Constant Integer
| Var Identifier
| Op OpName [Expr]
deriving (Show)

data Program = Identifier := Expr
| Block [Program]
| While Expr Program
| If Expr Program
| IfElse Expr Program Program
deriving (Show)
“`
Notice that we are using a constructor `:=` in the `Program` type, written in infix notation.
We use [monadic parsing](/LectureNotes/Sections/monads.md#monadic-parsing) to convert from [concrete syntax](ConcreteSyntax.md) to abstract syntax.

#### Next: [Parser](Parser.md)